HEARING. 241 



awakened, for a slight noise will often rouse a sleep- 

 walker, who had borne an intense light on his un- 

 shut eyes without seeming in the least to feel its 

 influence. 



The structure of the ear in birds would lead us 

 to conclude that they could not hear so quickly as 

 other animals. Nevertheless, we find that the sense 

 of hearing is enjoyed in an exquisite degree in birds ; 

 that the organ of the sense is not imperfect, but is 

 adapted to a new construction, and a varied appara- 

 tus suited to the condition of the bird ; and that 

 there is no accidental dislocation or substitution of 

 something less perfect than what we find in other 

 classes of animals."* 



The internal parts of the ear in birds are much 

 less complicated than in man and quadrupeds ; but, 

 without going into the minute particulars of differ- 

 ence, we shall only mention one peculiarity, which 

 is, that while the chamber of the drum communi- 

 cates with three large cavities in the adjacent bony 

 plates, these again communicate by an equal num- 

 ber of openings with the drum in the same side, one 

 of them extending over the scull to its fellow on 

 the other side. Sir Everard Home has observed a 

 similar kind of communication by means of the 

 cells of the scull in the elephant. We have little 

 doubt that the provision made for rendering birds 

 more buoyant, consisting of air-vessels extended 

 from the lungs throughout the body, and even to the 

 bones themselves, contributes to render the vibra- 

 tions of the air more distinct, muffled as they must 

 always partially be by the feathers of the bird. 



The faculty of imitating sounds possessed by cer- 

 tain birds, proves that their hearing must be ex- 

 ceedingly delicate ; and though we suspend our be- 

 lief of the great musical talents which some birds 

 are said to have derived from education, we find 



* Bridgewater Treatise on the Hand, p. 139. 

 X 



